Sometimes
history jumps. Think of the first world war, the Bolshevik
revolution, the Great Depression, the election of Adolf Hitler, the
second world war, the beginning of the cold war, the collapse of the
European empires, Deng Xiaoping’s “reform and opening up” of
China, the demise of the Soviet Union, and the financial crisis of
2007-09 and subsequent “great recession”.

We
may be on the brink of an event as transformative as many of these:
the election of Donald Trump as US president.This would mark the end
of a US-led west as the central force in global affairs. The result
would not be a new order. It would be perilous disorder.

The
fact that Mr Trump can be a credible contender for the presidency is
astounding. In business, he is a serial defaulterand litigator turned
reality TV star.

He is a peddler of falsehoods and conspiracy
theories. He utters racist calumnies.

He attacks the independence of
the judiciary. He refuses to reveal his taxes. He has no experience
of political office, and incoherent policies. He glories in
ignorance. He even hints at a federal default. He undermines
confidence in the US-created trade order, by threatening to tear up
past agreements. He undermines confidence in US democracy by claiming
the election will be rigged.

He supports torture and the deliberate
killing of the families of alleged terrorists. Headmires the former
KGB agent who runs Russia.

Evidently,
a huge number of US voters have lost confidence in the country’s
political and economic systems. This is so to an extent not seen even
in the 1930s, when voters turned towards an established politician.
Yet, for all its challenges, the US is not in such terrible shape. It
is the richest large country in the history of the world. Growth is
slow, but unemployment is low. If voters were to choose Mr Trump —
despite his failings, displayed again in the first presidential
debate — this would tell us grim things about the health of the US.

It
is the world’s leading power, so this is not just a domestic US
concern. What might a Trump presidency mean? Forecasting the policies
of someone so unpredictable is impossible. But a few things seem at
least reasonably clear.

The
US and its allies remain immensely powerful. But their economic
dominance is in slow decline. According to the International Monetary
Fund, the share of the high-income countries (essentially, the US and
its chief allies) will fall from 64 per cent of global output
(measured at purchasing power) in 1990 to 39 per cent in 2020, while
the US share will fall from 22 per cent to 15 per cent over this
period.

While
the US military might is still huge, two caveats must be made. One is
that winning a conventional war is quite a different matter from
achieving one’s aims on the ground, as the Viet­nam and Iraq
wars showed. Furthermore, China’s rapidly rising defence spending
could create serious military difficulties for the US in the
Asia-Pacific region.

It
follows that the ability of the US to shape the world to its liking
will rest increasingly on its influence over the global economic and
political systems. Indeed, this is not new. It has been a feature of
US hegemony since the 1940s. But this is even more important today.
The alliances the US creates, the institutions it supports and the
prestige it possesses are truly invaluable assets.

All such strategic
assets would be in grave peril if Mr Trump were to be president.

The
biggest contrast between the US and China is that the former has so
many powerful allies. Even Vladimir Putin is not a reliable ally for
China. America’s allies support the US largely because they trust
it. That trust is based on its perceived commitment to predictable,
values-based behaviour. Its alliances have not been problem-free, far
from it. But they have worked. Mr Trump’s cherished
unpredictability and transactional approach to partnerships would
damage the alliances irreparably.

A
vital feature of the US-led global order has been the role of
multilateral institutions, such as the IMF, the World Bank and the
World Trade Organisation. In binding itself by the rules of an open
economic system, the US has encouraged others to do the same. The
result has been extraordinary growth in prosperity: between 1950 and
2015, average global real output per head rose sixfold. Mr Trump does
not understand this system. The results of repudiation could be
calamitous for all.

The
Iraq war has damaged trust in US wisdom and competence. But the
global financial crisis has been even more destructive. Many have
long suspected US motives. But they thought it knew how to manage a
capitalist system. The crisis devastated that confidence.

After
all this damage, election of a man as unqualified as Mr Trump would
call into question something even more fundamental: belief in the
capacity of the US to choose reasonably well-informed and competent
leaders. Under a President Trump, the democratic system would lose
much of its credibility as a model for the organisation of a
civilised political life. Mr Putin and other actual or would-be
despots would cheer. Their belief that talk of western values is just
hypocrisy would be vindicated. But those who see the US as a bastion
of democracy would despair.

If
Mr Trump were to win, it would be a regime change for the world. It
would, for example, end efforts to manage the threat ofclimate
change, possibly forever. But even his candidacy suggests that the US
role in the global order risks undergoing a transformation. That role
depended not only on American economic and military prowess, but also
on the values it represented. For all its mistakes, the ideal of a
law-governed democratic republic remained visible. Hillary Clinton is
an imperfect candidate. Mr Trump is something else altogether. Far
from making America great, his presidency might unravel the world.

So
that's it y'all - vote for the corrupt, serial warmonger or the world
gets it!